1. ULTRA FINE GRAIN IN PLAIN C-MnSTEELS WITH 0.15-0.3% C R. Song, D. Ponge, D. Raabe

2. ? Why do we study ultra fine grained steel?

3. The reason is The development of industry needs a steel with advanced mechanical properties Grain refinement is the only method to improve both strength and toughness That is because ......

4. Hall-Petch relationship Ferrite Grain Size, d (µm) 40 10 5 3 1 900 800 700 600 500 400 300 200 0 - 40 - 80 -120 -160 -200 -240 Ultra fine grain Normalizing TMCP 50% FATT, (0C) Yield Strengh (MPa) 2 6 10 14 18 22 26 30 34 d-1/2 (mm-1/2)

5. How to get ultra fine grained steel?

6. High demands on the novel UF routes Niikura et al.

8. To determine the relationship between micro-structure and mechanical properties of UF grained steel

10. The effect of microstructure on strength Ferrite Grain Size, µm 20 10 5 2 1 0.5 800 700 600 500 400 300 0.15C-0.3Si-1.5Mn Steel ferrite+ cementite ferrite + pearlite Yeild Strengh, MPa +>300MPa Conventional Grain Size Ultrafine Grain Size 104 106 108 1010 Number of Grains in 1 mm3 K. Nagai

11. The PonyMILL processing route Conventional Hot Mill Line Coiler Run out table Coil Handling Coil Transfer PonyMILL Single High Reduction Stand Un-Coiler Re-Coiler

14. Experiment machine The Hot Working Simulator (WarmUMformSImulator) W SI UM “WUMSI”

15. Experiments from WUMSI Microstructure Investigation Cuboid Sample

16. Experimental routes hot deformation (conventional hot strip mill) =0.3, =10s-1 holding compression 2min =4×0.4, =10s-1 air cooling simulated final coiling A3 5~12℃/s 50℃/s PF BS heavy warm deformation (PonyMILL) Pearlite route BainiterouteⅠ Bainiteroute Ⅱ

17. Optimum austenite deformation temperature Optimization of deformation temperature in austenite region (WUMSI) Water quenched microstructure after deformation at 860℃ of 0.15%C steel Tg=Ae3+100℃ for 3 min air Tde compression =0.3, =10s-1 water

18. Selection of cooling rate to get desired initial microstructure (F+P or B) Experiment schedule (deformation dilatometry) Changes in microstructure and hardness of experimental steels with different cooling rates Tg =Ae3+100℃ for 3 min air compression Ar3 cooling 64...2℃/s M+B+F F+P +B +M UTS, F+P+B F+P

19. DCCT diagram of the steels DCCT diagram (ferrite + pearlite region) of 0.15%C, 0.2%C and 0.3%Csteel DCCT diagram of 2CMsteel BR II PR BR I

20. Starting temperature of heavy deformation Effect of heavy deformation temperature on flow curves and temperature increase in 0.3%C steel 500℃de 600℃de 700℃de 730℃de

21. The effect of heavy deformation temperature on microstructure 5000C-coiling 5500C-coiling 6000C-coiling 7000C-coiling 5500C 6000C 6400C 7000C bainite route I ND bainite route II

22. (a) grain size: 3.50µm (b) grain size: 1.25µm The effect of heavy deformation temperature on the microstructure in 0.3%C steel 7000C 85-95% are high angle boundaries 5000C

24. equiaxed grains

26. Microstructure evolution during compression in PR short pearlitic fragments pearlitic ferrite compression compression pearlitic ferrite pro-eutectoid ferrite with subgrains pearlitic cementite lamella pro-eutectoid ferrite new ferrite grains 1m 1m 2m

27. SEM micrographs of 0.3%C steel after bainite routeⅠ Substructure in large grains subgrains large grain Heavy deformation at 500℃ and subsequent simulated coiling at 700℃

28. Low angle misorientation

29. * deformation temperature (PR and BR II) or simulated coiling temperature (BR I) Micro-hardness for different routes

31. Three new process routes for heavywarmdeformation have been designed and employed to obtain UFG steel

34. L. Storojeva, D. Ponge, D. Raabe, R. Kaspar: Z. Metallkunde 95 (2004) 1108-1114, On the influence of heavy warm reduction on the microstructure and mechanical properties of a medium carbon ferritic-pearlitic steel

35. R. Song, D. Ponge, D. Raabe, R. Kaspar: Acta Mater. 53 (2004) 845858, Microstructure and crystallographic texture of an ultrafine grained C-Mn steel and their evolution during warm deformation and annealing

36. R. Song, D. Ponge, D. Raabe: ScriptaMaterialia 52 (2005) 1075-1080, Improvement of the work hardening rate of ultrafine grained steels through second phase particles

37. R. Song, D. Ponge, D. Raabe: ISIJ International 45 (2005) 1721-1726, Influence of Mn Content on the Microstructure and Mechanical Properties of Ultrafine Grained C-Mn Steels

38. R. Song, D. Ponge, D. Raabe: Acta Mater. 53 (2005) 4881-4892, Mechanical properties of an ultrafine grained C­Mn steel processed by warm deformation and annealing

39. R. Song, D. Ponge, D. Raabe, J.G. Speer, D.K. Matlock: Mater. Sc. Engin. A 441 , 2006) 1–17, Overview of processing, microstructure and mechanical properties of ultrafine grained bcc steels